PROJECT SUMMARY/ABSTRACT Lung cancer is the leading cause of cancer-related mortality in the United States. The overall 5-year survival of patients diagnosed with lung cancer is 18%, and outcomes for advanced stage patients treated with standard chemotherapies have plateaued. Recent discoveries of genetic alterations in receptor tyrosine kinases such as Epidermal Growth Factor Receptor (EGFR) have led to development of tyrosine kinase inhibitors as lung cancer therapies. However, intrinsic and acquired resistance to inhibitors is currently a major problem in the clinic, making development of novel therapies for lung cancer imperative. Histone modifications, including lysine acetylation, play crucial roles in transcriptional activation and elongation, gene silencing and epigenetic cellular memory, and aberrant epigenetic changes are associated with oncogenesis. Among epigenetic modifiers, aberrant activity of several lysine (K) acetyltransferases (KATs) is implicated in cancer development. To assess the function of one of those acetyltransferases (KAT5) in lung cancer, we generated conditional Kat5 knockout mice and found that lung-specific Kat5 deletion suppressed tumor formation induced by EGFR-L858R-T790M. We also showed that mutant EGFR bound to and tyrosine-phosphorylated KAT5 at two tyrosine residues in the catalytic domain, increasing its acetyltransferase activity. Thus, we hypothesize that KAT5 is required for lung tumorigenesis induced by oncogenic kinases such as EGFR mutants. In Aim 1, we will investigate how KAT5 tyrosine phosphorylation increases its acetylase activity and whether oncogenic kinases such as mutant EGFR induce KAT5 activation in lung cancer. In Aim 2, we will investigate whether KAT5 regulates Wnt/?-catenin signaling, which is crucial for lung tumorigenesis by activating EGFR mutations. In addition, we will identify KAT5 effectors potentially responsible for tumorigenesis using biochemical analysis plus a combination of RNA sequencing and chromatin immunoprecipitation sequencing. In Aim 3, we will ask whether KAT5 is required for tumor initiation, maintenance of established lung tumors, or both, using transgenic mouse models. Aim 3 also addresses a potential function for KAT5 in proliferation and self-renewal in lung cancer stem/initiating cells. Experiments proposed here should lead to development of novel epigenetic therapies and significantly impact care of patients with lung cancer, particularly those with unfavorable prognosis, in the near future.